1. Field of the Invention
The invention concerns an extruder for producing melts from commercially available granulated plastics by heating and milling the granules by means of heated single-screw or twin-screw extruders, for carrying out condensation polymerization or polymerization by using a section of the extruder that is designed as a multi-screw extruder, with the use of evacuated chambers for removing low-molecular-weight constituents and/or blowing agents or the like, for obtaining larger molecules and thus higher viscosities, and for increasing the mechanical strength of the plastic produced from the melt.
2. Description of the Related Art
Commercial granulated plastics can be processed into melts in a single-screw extruder, which is suitable, for example, for the injection of plastic articles, but is also suitable for drawing filaments. However, thin plastic sheets require a tougher and stronger raw material to allow their further processing. In this regard, it is known that the single-screw extruder can be connected to venting devices, as described, for example, in the prior-art document EP 0 588 998 A1, in which raw materials of this type can be produced by passing the plastic melt through evacuated chambers. The removal of low-molecular weight constituents, such as glycol or the like, can be accomplished here by prolonged residence times of thin layers of melt in evacuated chambers. Similar venting units are disclosed, for example, in DE 100 20 646 C1 and DE 40 01 986 (U.S. Pat. No. 5,108,711). Of course, in the systems described here, the disadvantages of the relatively complicated design of the assemblies with intermeshing shafts are readily apparent, as are the disadvantages associated with the relatively high production cost of the extruder and the venting unit.